Gene expression is regulated, in part, by the cellular processes involved in transcription. During transcription, a single-stranded RNA complementary to the DNA sequence to be transcribed is formed by the action of RNA polymerases. Initiation of transcription in eukaryotic cells is regulated by complex interactions between cis-acting DNA motifs, located within the gene to be transcribed, and trans-acting protein factors. Among the cis-acting regulatory regions are sequences of DNA, termed promoters, to which RNA polymerase is first bound, either directly or indirectly. As used herein, the term “promoter” refers to the 5' untranslated region of a gene that is associated with transcription and which generally includes a transcription start site. Other cis-acting DNA motifs, such as enhancers, may be situated further up-and/or down-stream from the initiation site.
Both promoters and enhancers are generally composed of several discrete, often redundant elements, each of which may be recognized by one or more trans-acting regulatory proteins, known as transcription factors. Promoters generally comprise both proximal and more distant elements. For example, the so-called TATA box, which is important for the binding of regulatory proteins, is generally found about 25 basepairs upstream from the initiation site. The so-called CAAT box is generally found about 75 basepairs upstream of the initiation site. Promoters generally contain between about 100 and 1000 nucleotides, although longer promoter sequences are possible.
For the development of transgenic plants, constitutive promoters that drive strong transgene expression are preferred. Currently, the only available constitutive plant promoter that is widely used is derived from Cauliflower Mosaic Virus. Furthermore, there exists a need for plant-derived promoters for use in transgenic food plants due to public conceptions regarding the use of viral promoters. Few gymnosperm promoters have been cloned and those derived from angiosperms have been found to function poorly in gymnosperms. There thus remains a need in the art for polynucleotide promoter regions isolated from plants for use in modulating transcription and expression of polynucleotides in transgenic plants.